Device for adjusting the measurement range of captors fitted with force balances particularly for pressure conveyors

ABSTRACT

The device comprises a force balance including several windings, switches being provided for selective connection of any of the windings in the circuit of the force balance to compensate for different ranges of measurement.

4 United States Patent 1151 3,660,745 Bertrand [4 1 May 2, 1972 [541DEVICE FOR ADJUSTING THE 58 Field of Search ..73/39s R, 407, 141, 141 R;MEASUREMENT RANGE OF CAPTORS 336/30; 177/212; 346/32; 317/155.5; 38/645; FITTED WITH FORCE BALANCES 316/676 687 PARTICULARLY FOR PRESSURE56] References Cited CONVEYORS [72} Inventor: Pierre Claude Bertrand,Pau-Billere, UNITED STATES PATENTS France 3,350,945 l l/l967 Bristol..73/398 [73] Assigneez compagnie Des comptgurs, Paris' France 3,376,4824/l968 Barthel .318/676 [22] l l June 5, 1970 Primary Examiner-Donald O.Woodiel [211 App], No: 43,849 A1mr11eyPierce, Scheffler& Parker [57]ABSTRACT [30] Foreign Application Priority Data The dev1ce comprises aforce balance 1nclud1ng several June 19, 1969 France ..6920508 i di with b i g r vided for selective connection of any of the windings in thecircuit of the force balance to com- [52] US. Cl. ..3l8/676, 73/398 R,73/407, pensate f diff t ranges f measurement 318/645, 318/687 [51] Int.Cl. ..G01l 9/ 10 6 Claims, 2 Drawing Figures Patented -May 2, 1972 2Sheet et 1 I II L Paten ted May 2, 1972 2 Sheets-Sheet 2 FI'GB.

DEVICE FOR ADJUSTING THE MEASUREMENT RANGE OF CAPTORS FITTED WITH FORCEBALANCES PARTICULARLY FOR PRESSURE CONVEYORS In many technical fieldsand, more particularly, in force balances of the type which are designedfor the measurement of differential pressures, it is highly desirablethat a given equipment may be regulated without being subject toconstructional alterations, and this, while said equipment is soconceived that it may be used with the same accuracy for the measurementof different scale magnitudes. This is the case, particularly, withmeasurement devices for differential pressures wherein the equipmentmust often be able to work within quite difi'erent ranges, whethersimilar mass produced equipments are used in some parts of plantswherein prevail different conditions, or that one equipment only is tobe used seriatim for the measurement or for the detection of saiddifferent magnitudes.

The invention has been conceived and developed to provide a new devicefor adjusting the measurement range of apparatus fittedwith forcebalances, whereby it is possible to make measurements, checkings orother operations relating to magnitudes, particularly the measurement ofpressures capable of considerable variations. I

According to the invention, the device is characterized in that aresetting means of the force balance is made of several winding unitswith the number of turns set according to a given ratio, said windingsbeing connected to a power supply and to a load through a drivenamplifier, and switches being designed for the selective connection ofany number of said winding units in the circuit of said load.

Besides, the invention also extends to the working out of a forcebalance for the measurement of differential pressures and allows, by theoperation thereof, an easy and economical construction of said balance.I

Various other features of the invention appear from the detaileddescription made hereinafter.

Embodiments of the invention are shown, as non-restrictive examples, onthe accompanying drawing.

FIG. 1 is a diagrammatic sectional view in elevation of a force balancepressure measurement device.

FIG. 2 is an electrical diagram showing an embodiment of a regulationdevice of the measurement scale for differential pressures measured bythe balance shown on FIG. 1.

The force balance for the measurement of differential pressures as shownon FIG. 1, includes a casing 1 wherein is set a transverse partition 2which bears a port-hole 3. Two diaphragms 4 and 5, respectively, made ofdistortable membranes define with side walls 121 and 1b, of casing 1respectively, chambers 6 and 7 designed for the containing of fluidssubject to variable pressures which are admitted to said chambersthrough intake ducts 8 and 9, respectively, which are set in the sidewalls la, lb ofthe casing.

It is assumed hereinafter, as an example, that chamber 6 is intended tocontain a fluid under a lower pressure than chamber 7, it beingunderstood that it may be the inverse without causing any change in theworking of the balance.

A distortable bellows 10 is secured to partition 2 about the port-hole 3and is closed at its opposite end by a plate 11 which is connected bymeans of a strut 12 to a rotatable arm 13 serving as a balance-beam,which is mounted on a rod 14 supported, for instance, by casing 1. Arm13, serving as the balance-beam, carries, at the side opposite to thatconnected to strut 12, one or several coils 15 which are described indetail hereinafter, said coils being set into the gap 16 of a mag neticcircuit similar, for instance, to the magnetic circuit of a loud speakerand whose various components thereof are referenced under number 17,said magnetic circuit being with an incompressible fluid, oil forinstance, so that whenever, as explained above, a pressure is createdin-chamber 7 which is higher than that in chamber 6, diaphragm 5 tendsto become distorted, which causes also the distorsion of bellows l0,and, thereby permits part of the incompressible fluid it contains topass through port-hole 3 causing as a result the distorsion of diaphragm4. This causes arm 13 to rotate clockwise about rod 14, since said armis connected to plate 11 through strut 12. Rotation of arm 13 isobviously detected by the magnetic detector including circuit 20 andcoil 21 and, as described hereinafter, said detection controls a feedingdevice for coils 15 so as to reset arm 13 to the initial or nullposition thereof wherein a zero reading is given by the magneticdetector 20, 21.

An embodiment of the device for resetting the arm 13, which forms thebalance-beam, to the balancing position thereof, is shown in FIG. 2which shows coils 15 made up in this case of several winding units 15a,15b ..lSn connected in series, i.e. said winding units are defined, forinstance, by a single winding separated by multiple plugs 22, 22a, 22b..22n which are connected by conductors 23, 23a, 23b ..23n to switches24a, 24b ..thereby allowing one to connect up selectively conductors 23to 23n or to short-circuit successive plugs 22, 22a ..22n and therebyconnecting up one or more or less perhaps none of the winding units 150to 15n. Preferably, the number of turns of the successive winding unitsshould be chosen according to a binary ratio, i.e. winding 15a willinclude a number of n turns, winding 15b a number of 2n turns, winding15 a number of 4n turns and so on, so as to allow, by arranging saidwinding units according to a given order, a plurality of regulationsstep by step.

As shown in FIGS. 1 and 2, windings 15 are fed from a power supply 26and through an amplifier 27 which also provides power to the magneticdetector winding 21, hereinabove described, and which is actuated inresponse to said magnetic detector, in such way that the output currentof the amplifier will feed one or several windings 15a l5n with anintensity high enough to balance the force exerted on bellows 10, theintensityof said current being detected or measured by a detector 28which may consist of an ammeter or by any other measurement device whichmay, should it so happen, be a servo-device of a control or checkingcircuit. Detector 28 should be considered in its broadest sense inasmuchas its function may be a measurement function aswell as detection one.

Assuming that force, balance, FIG. 1, were to detect and measuredifferential pressures ranging, for instance, between 0 and 1, the lowpressure alone said pressure range being exerted in chamber 6 and thehigh pressure in chamber 7, then winding unit 15a alone could be used,which is fact, by leaving switch. 24a open and closing all the otherswitches shown in FIG. 2.

If, on the contrary, the pressure difference between chambers 6 and 7ranges between 0 and 2, then winding unit 15b along may be used byclosing switch 24a, while leaving open switch 24b and by closing all theother switches. As a matter of act, this is feasible because the ratioof number of turns between winding units 15a and 15b is a binary ratio,which allows besides, for example, if the pressure difference in chambers 6 and 7 varies from O to 3 to use, winding units 150 and 15b, whileexcluding the others.

Assuming now that the pressure difference in chambers 6 and 7 were torange between zero and a-number including a decimal, 3.50 for instance,then, as explained above, winding units 15a and 15b will be switched onand potentiometer 25 will be set in such a position that it willpartially short-circuit winding .15n.

It is worth noticing that owing to the arrangement by which all windingunits, regardless of their design are housed inside the force balanceitself, i.e. more precisely into the space filled up with theincompressible fluid, casingl can have sealed openings for entry of theconducting wires without any mechanical part passing through saidcasing. Furthermore,

temperature variations have thus no effect on the windings and anytemperature variations said windings may sustain have no effect on theaccuracy of the measurements.

Although only one form of the invention has been illustrated, it isobvious that various changes and modifications may be made withoutdeparting from the spirit of the invention and all of such changes arecontemplated as may come within the scope of the claims. Switches 24a,24b and so on, particularly, may be replaced by any other technicalmeans, by staples, tommy-bars for instance or even by welding, once thedevice is finally adjusted. Besides, switches or substitutes thereof mayequally be set at various places, on the casing, for instance, when theyare on the outer part thereof or directly on the coil or thebalance-beam if they are set inside the casing.

I claim:

1. In a force balance of the type comprising a balance-beam subjected toa displacement in accordance with a change in magnitude of a variableforce to be measured and wherein said displacement is measured as afunction of the force required to rebalance the beam, the improvementcomprising a magnetically operated device for establishing therebalancing force, said device including a winding comprising aplurality of coils having a predetermined turn ratio and which can beselectively connected in series, the number of coils in series circuitdetermining the force for rebalancing the balancebeam, switch meansassociated with each coil for selectively connecting the same into saidseries circuit, a power supply for feeding said series connected coils,circuit means including an amplifier for connecting the power supply tothe series connected coils and means for controlling the amplificationfactor in proportion to the displacement of said balance-beam.

2. In a force balance as claimed in claim 1 wherein each of said switchmeans is connected across the end terminals of the appertaining coil.

3. In a force balance as claimed in claim 1 wherein the number of turnsof the coils are chosen according to a binary ratio and furthercomprising a variable resistor connected in parallel to one of saidcoils whereby the force exerted by said one coil may be adjusted to avalue between zero and the maximum force exertable thereby.

4. In a force balance as claimed in claim 1 wherein the coils may beselectively coupled in series and wherein said switches short-circuitsaid coils when closed and further comprising a variable resistorconnected in parallel to one of said coils for adjusting the forceexerted by said one coil between zero and the maximum force exertablethereby.

5. In a force balance as claimed in claim 1 wherein said coils areassociated with the balance beam and the circuit means including anamplifier also includes a detector for sensing the position of thebalance beam.

6. A force balance for determining fluid pressure differentials by aservo-rebalance system comprising a casing having opposed fluid portstherein, two distortable spaced parallel diaphragms mounted in saidcasing between said fluid ports, a fixed partition between saiddisphragms provided with a port therethrough, a bellows element mountedon said partition and surrounding said port on one side thereof, amagnetically operated device mounted on the same side of the partitionas said bellows for establishing a rebalancing force, a balance-beampivotally mounted adjacent said bellows and said magnetic device, onearm of said balance-beam being connected to said bellows to actuate samewhen said beam is pivoted, a plurality of coils connected to the otherarm of the beam and having a predetermined turn ratio and which can beselectively connected in series, the number of coils in series circuitdetermining the force for rebalancing the balancebeam switch meansassociated with each coil for selectively connecting the same into saidseries circuit, a power supply connected to an amplifier for feedingsaid series connected coils, the space between said spaced diaphragms inwhich said balance-beam, said magnetic device, said plurality of coilsand said bellows are disposed being filled with an incompressibleliquid, whereby variations in the pressure of the fluid entering one ofsaid fluid ports will distort said spaced diaphragms and thus actuatesaid balance-beam, and magnetic detector means responsive to movement ofsaid balance beam for controlling the amplification factor of saidamplifier and accordingly the current to at least one of said coils torestore the balancebeam to a null position and means for measuring theamount of current required.

1. In a force balance of the type comprising a balance-beam subjected toa displacement in accordance with a change in magnitude of a variableforce to be measured and wherein said displacement is measured as afunction of the force required to rebalance the beam, the improvementcomprising a magnetically operated device for establishing therebalancing force, said device including a winding comprising aplurality of coils having a predetermined turn ratio and which can beselectively connected in series, the number of coils in series circuitdetermining the force for rebalancing the balance-beam, switch meansassociated with each coil for selectively connecting the same into saidseries circuit, a power supply for feeding said series connected coils,circuit means including an amplifier for connecting the power supply tothe series connected coils and means for controlling the amplificationfactor in proportion to the displacement of said balance-beam.
 2. In aforce balance as claimed in claim 1 wherein each of said switch means isconnected across the end terminals of the appertaining coil.
 3. In aforce balance as claimed in claim 1 wherein the number of turns of thecoils are chosen according to a binary ratio and further comprising avariable resistor connected in parallel to one of said coils whereby theforce exerted by said one coil may be adjusted to a value between zeroand the maximum force exertable thereby.
 4. In a force balance asclaimed in claim 1 wherein the coils may be selectively coupled inseries and wherein said switches short-circuit said coils when closedand further comprising a variable resistor connected in parallel to oneof said coils for adjusting the force exerted by said one coil betweenzero and the maximum force exertable thereby.
 5. In a force balance asclaimed in claim 1 wherein sAid coils are associated with the balancebeam and the circuit means including an amplifier also includes adetector for sensing the position of the balance beam.
 6. A forcebalance for determining fluid pressure differentials by aservo-rebalance system comprising a casing having opposed fluid portstherein, two distortable spaced parallel diaphragms mounted in saidcasing between said fluid ports, a fixed partition between saiddisphragms provided with a port therethrough, a bellows element mountedon said partition and surrounding said port on one side thereof, amagnetically operated device mounted on the same side of the partitionas said bellows for establishing a rebalancing force, a balance-beampivotally mounted adjacent said bellows and said magnetic device, onearm of said balance-beam being connected to said bellows to actuate samewhen said beam is pivoted, a plurality of coils connected to the otherarm of the beam and having a predetermined turn ratio and which can beselectively connected in series, the number of coils in series circuitdetermining the force for rebalancing the balance-beam switch meansassociated with each coil for selectively connecting the same into saidseries circuit, a power supply connected to an amplifier for feedingsaid series connected coils, the space between said spaced diaphragms inwhich said balance-beam, said magnetic device, said plurality of coilsand said bellows are disposed being filled with an incompressibleliquid, whereby variations in the pressure of the fluid entering one ofsaid fluid ports will distort said spaced diaphragms and thus actuatesaid balance-beam, and magnetic detector means responsive to movement ofsaid balance beam for controlling the amplification factor of saidamplifier and accordingly the current to at least one of said coils torestore the balance-beam to a null position and means for measuring theamount of current required.